When you try to use Microsoft Outlook to perform an action on a calendar meeting item in a Microsoft Office 365 environment, you receive the following error message:
This message could not be sent because it exceeds the maximum size allowed.
This error occurs if one of the following conditions is true:
One or more file attachments in the meeting item made the message size too large.
The reminder for the meeting item is corrupted.
To fix this issue, delete that particular meeting item by using Microsoft Exchange Server MAPI Editor (MFCMAPI). To do this, follow these steps.
Note Although the MFCMAPI tool is supported by Exchange Online, we recommend that you always use caution when you modify mailboxes by using this tool. Using the MFCMAPI tool incorrectly can cause permanent damage to a mailbox. Confirm that Outlook is set to use Cached Exchange Mode before you perform this procedure.
Download and install MFCMAPI from the following Microsoft CodePlex website: